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  <script>
    let array = [1, 1, 2, 3, 3, 4, 4, 4, 5]
    var res = [];
    for (let i = 0; i < array.length; i++) {
      //查看第一次出现和最后一个是否全等
      if (array.indexOf(array[i]) === array.lastIndexOf(array[i])) {
        res.push(array[i]);
      }
    }
    console.log(res)


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